article: The first time I went abroad was when I went to London. It was in the summer holidays about five or six years ago and I went with three friends. The plane and train were quite expensive, so we decided to travel by coach. We left at five o'clock in the morning and the journey to London took about sixteen hours but we didn't mind: we were all very excited because for all four of us it was our first time away from home.
  We stayed in London for three days, in a youth hotel not far from the centre. While we were there, we walked a lot. First, we went to see all the famous sites--Big Ben, Piccadilly Circus, Buckingham Palace, then we went shopping in Oxford Street. On the last morning my friends stayed in bed late, but I got up early and went to Camden Market. You can buy all kinds of jewelry and clothes there, and I bought a silver ring for my sister. It was really hot in the afternoon, so we went to Hyde Park for a game of football. Unfortunately, I think the ring fell out of my pocket during the game, because I couldn't find it when I got on the coach that evening!
  I've been back to London several times since then, but I don't think I'll ever feel as excited as I did that first time.
question: When did the wrier think he lost the silver ring he bought for his sister?
options: When they went shopping in Oxford Street. When they played football in Hyde Park. When he got on the coach that evening. When he got back to London.